1. Field of the Invention
The present invention relates to an air conditioner using a compressor driven variably in revolution number by an inverter, in particular, to an air conditioner which is able to shorten a necessary time until a room temperature comes up to a preset temperature after initiating a heating operation, or which is constructed by combining an electric motor and a refrigerating cycle so as to obtain a comfortable heating operation in a cold district, and an electric motor used therefor.
2. Description of Prior Art
In a conventional air conditioner, for reducing an electric power consumption, an improvement in a performance was made especially in a low range of a revolution number of a compressor where there is not necessitated relative large capacity. As an example of such recent technology for improvement of the performance, a technology in which the revolution number of the electric motor for driving a compressor is variably controlled by an inverter of PWM (Pulse Width Modulation) control can be listed. With the PWM control, it is intended to increase an efficiency without increasing a drive torque so much.
And, there is also known an air conditioner which is adopted to a relative low temperature of an outside air or a large drive load of the heating operation by using a compressor of large capacity in refrigerant compression corresponding to a drive load.
In case that the temperature of the outside air is low or that the necessary heating capacity is large, an ejection pressure of the refrigerant increases and a condensation pressure of an interior heat exchanger also comes up to be high. For reducing the condensation pressure, it can be considered that the above condensation pressure is made small by increasing the heat transmitting or exchanging area of the interior heat exchanger so as to make easy to condense the refrigerant gas, thereby reducing the drive torque of the electric motor and increasing the efficiency.
As an example of a conventional art to control the revolution number of the electric motor so as to increase the efficiency, followings are known. As an example of an electric motor driving apparatus of conventional art is shown, for example in Japanese Patent Publication No. Hei 7-89743 (1995), in which as an electric power source is adopted an electric power converter of a high power factor which can suppress high harmonics in an input current. In FIG. 12 showing an block diagram of such the conventional electric motor driving apparatus, a reference numeral 1 depicts a a-c power source, 2 a rectifier, 2a, 2b, 2c and 2d diodes, 3 a reactor, 4 a diode, 5 a condenser, 6 a switching element, 7 a voltage comparator, 8 a multiplier, 9 a load current detector, 10 a current compactor, 11 an oscillator, 12 a driver circuit, 13 an inverter, 14 an electric motor, 15 a micro computer, 16 an inverter driver circuit, and 17 a modulator. In the same dawning, a portion, including the rectifier 2, the reactor 3, the diode 4, the condenser 5, the switching element 6, the voltage comparator 7, the multiplier 8, the load current detector 9, the current comparator 10, the oscillator 11, the driver circuit 12 and the modulator 17, constitutes an electric power converter, and the inverter uses the electric power converter as the power source thereof.
First, an explanation will be given on the electric power converter.
The a-c power voltage from the a-c power source 1 is rectified in full-wave by the rectifier 2 constructed with those diodes 2a through 2d, and converted into a rectified voltage Es. The rectified voltage Es is applied to the condenser 5 through the reactor 3 and the diode 4, thereby a smoothed d-c voltage Ed can be obtained. In parallel to those diode 4 and the condenser 5, the switching element 6 is provided.
The smoothed d-c voltage Ed with the condenser 5 is divided by resistors R3 and R4 so as to form a d-c voltage Ed', and the difference between this and a reference voltage Eo is obtained by the voltage comparator 7 so as to form a voltage controlling signal Ve.
The rectified voltage Es, which is obtained through the full-wave rectification of the a-c power source voltage of the sinusoidal wave-form by the rectifier 2, is also divided by the resistors R1 and R2 so as to form a synchronizing signal Es' of the sinusoidal wave-form, and the sinusoidal synchronizing signal Es' is calculated with the voltage controlling signal Ve from the voltage comparator 7 by the multiplier 8 to form a current reference signal Vi'. The current reference signal Vi' is compared with a current signal Vi obtained by the load current detector 9 in the current comparator 10 so as to obtain a modification signal Vk. The modifier 17, to which the modification signal Vk is supplied, modifies a carrier wave of a saw-tooth or a triangle wave-form from the oscillator 11 to form a switching drive signal Vg of so called a PWM (Pulse Width Modulation) where a duty ratio is changed depending on the modification signal Vk. On the modification signal Vk, the driver circuit 12 drives the switching element 6 into ON or OFF state.
As is mentioned above, in the conventional art, the switching element 6 is driven ON or OFF following the wave-form of the sinusoidal rectifier voltage Es, thereby it is possible to obtain the sinusoidal current of less high harmonic wave components and of high power factor as the input a-c current. And, the commutation rate of the switching element 6 is changed depending on the difference between the reference voltage Eo and the d-c voltage Ed, thereby it is possible to obtain a stable d-c voltage Ed irrespective of a fluctuation of the load. Consequently, it is said, by setting the reference voltage Eo and the resistance value of the resistors R3 and R4 appropriately, it is possible to set the d-c voltage Ed at a desirable voltage value, and to convert an input a-c electric power into a d-c output.
Next, an explanation will be given on an electric motor driver circuit shown in FIG. 12.
The d-c electric power produced with the above electric power converter is inverted into the a-c electric power through the inverter 13, and it is supplied to drive the electric motor 14. And, the inverter 13 is supplied with the PWM signal which is calculated and outputted from the micro computer 15 on the basis of a speed instruction through the inverter driver circuit 16, thereby the inverter 13 is driven so as to drive the switching element (not shown in drawing) into ON or OFF at a predetermined commutation ratio.
Next, as a conventional air conditioner in which the heat exchanging area of the interior heat exchanger is enlarged, such as shown in "GD Series of An Air Conditioner of Low Energy Consumption Type Applying New Dehumidification Method", Toshiba Review, Vol. 51, No. 2, 1996, PP 67-70 (Document 1), recently, an air conditioner having such a construction that the interior heat exchanger is extended form a front surface of an interior machine to a back surface thereof, and an air conditioner in which an interior auxiliary heat exchanger being able to be used as an excess cooler under the heating operation is provided in down flow side of the interior heat exchanger, are developed.
The conventional arts of the mentioned-above has following drawbacks.
1) In case that the operation load is large, especially, when the air conditioner is operated for heating in a area of very cold temperature, such as the outside air temperature is -10.degree. C. or -15.degree. C. in the cold district, and in case that the room temperature is so decreases that the wall and the furniture therein are chilled when it is initiated to operate, in accordance with the revolution number control trying to increase the efficiency without increasing the drive torque so high by the above PWM control, because of shortage of the drive torque, it is impossible to rotate it at a necessary high revolution number, thereby failing to reach the preset temperature or necessitating a long time period to reach it.
2) In case that a compressor having large refrigerant compressing capacity corresponding to the operation load is used, if the outside air temperature is relative high and the load for the heating operation is small, the compressor is turned on and off since the operation capability is in excess. With the operation of turning on and off is increased the electricity consumption and a comfortableness is lost as well, since the room temperature is up and down.
3) In an air conditioner for home use, it is so designed that an upper limit is provided in the input current of the air conditioner in consideration with a capacity of an average capacity of a breaker circuit. From such the reason as well, the drive torque of mentioned-above cannot be increased so much.
4) When the outside air temperature is low, since the heating capability of necessity is large, the ejection pressure of the refrigerant from the compressor increases and the condensation pressure of the interior heat exchanger becomes high. Since work amount becomes large under the high condensation pressure, it results in an increase of the electric power consumption.
5) For reducing the electric power consumption, it is necessary to reduce the condensation pressure mentioned above. For that purpose, it is conceivable to increase the heat exchanging area of the interior heat exchanger, thereby making the condensation of the refrigerant gas easy. However, with the air conditioner, since the sizes of an standard interior machine are already determined in consideration with an installation and an interior wideness of a room, it is difficult to enlarge the area of the interior heat exchanger which directly relates to the sizes of the interior machine.
As is in the above, also in case of the air conditioner in which the interior heat exchanger is enlarged enough in the interior machine, and is further with the auxiliary heat exchanger, it is still needed to improve the heat exchanging efficiency in the interior heat exchanger in each of the cooling and heating operations as far as possible, thereby to maintain the efficiency of a refrigeration cycle at high, by designing piping construction of the interior heat exchanger and the relationship to an air flow thereof.
Explaining in more concretely, with the construction of the electric motor driver apparatus of the conventional art mentioned above, the d-c voltage Ed is obtained with stability irrespective of changing in the input a-c power voltage, however, in case that it is desirable to change the d-c voltage Ed depending on the voltage value of the input a-c power voltage, a circuit constant must be revised. In particular, for obtaining a stable control, since it is the electric power converter of a booster type in the prior art mentioned above, the d-c voltage Ed should be set as follows, with the equation below: d-c voltage Ed.gtoreq.a-c source voltage.times.1.41+10 V! if the input a-c source voltage is equal to 100 V, the d-c voltage Ed is set at equal or higher than 150 V, and if it is 200 V, Ed at equal or higher than 300 V, respectively.
Therefore, for obtaining the electric power converter which can be used in both 100 V and 200 V a-c power source 1, it is necessary to set the set value of the d-c voltage Ed at to be equal or higher than 300 V.
For example, in case of the 100 V input a-c source voltage, with a revolution control without the chopper of the 100% commutation rate and with an arbitrary d-c voltage Ed which is equal or higher than 150 V, a loss can be diminished, rather than through the revolution control with the constant d-c voltage Ed around 300 V and with chopper-driving of the inverter 13 at an arbitrary commutation rate. However, the above prior art never takes such the regard into consideration, therefore it has drawback that the loss becomes much more that that of necessary.
Further, with the above prior art, since it adopts a method, in which the input a-c current is controlled in the sinusoidal wave-form by referring the current reference signal Vi' which is produced by calculating in the multiplier 8 the voltage control signal Ve and the sinusoidal synchronization signal Es' which is formed by dividing the sinusoidal rectified voltage Es obtained by the full-wave rectification of the a-c source voltage from the a-c voltage source 1, if the a-c source voltage supplies 100 V and 200 V, the shape of the obtainable sinusoidal wave-forms differ in respective cases due to the difference in the rectified voltage Es. Because of this respect, if being used in common with the 100 V a-c source voltage and the 200 100 V a-c source voltage, it comes to be the electric power converter having a bad power factor and a high content rate of the high harmonics.
Moreover, with an electric motor driver apparatus or an air conditioner using such the electric power converter as mentioned in the above, if it is used with 100 V or 200 V of the a-c source voltage, the electric power converter must designed satisfying the specifications corresponding to them respectively. Therefore, it causes an increase in production types or variations, and a decrease in an efficiency of production or productivity thereof.
Furthermore, in case that the input a-c current is small, and, in particular that there is no need of such the control as mentioned above, on the contrary, there is not taken any consideration of removing or prohibiting from an unstable operation in control or loss, or noises when the input current is a low amount.
For example, when a resistor is used as the load current detector 9 to obtain the current signal Vi from a voltage appearing across the both ends of it, it is necessary to generate the voltage enough for the control even for a very small amount of current, and in concrete, it is necessary to set the resistance value of the resistor at a large value. In that case, however, an electric power consumed with the resistor becomes great and causes the increase in the loss, in particular when the load current comes to be a large amount.
Furthermore, with the inverter 13 in which the d-c source voltage Ed is constant, the electric motor 14 is rotated at a predetermined revolution number corresponding to the duty ratio which is determined by chopping the d-c source voltage Ed with the commutation ratio depending on the duty ratio of the PWM signal from the micro computer 15. Namely, in such the conventional electric motor driver apparatus in which the revolution number of the electric motor 14 changes depending on the change in the duty ratio, as mentioned above, the inverter 13 is always driven with the chopper operation, thereby causing the electric power loss (a chopper loss) and necessarily lowering the efficiency thereof.